U.S. Pat. No. 4,304,767 describes polymers of ketene acetals and polyols which are bioerodible and are suitable as carriers or matrices for therapeutic agents. These polymers containing entrapped therapeutic agents are bioerodible and when emplaced in a mammal they degrade and release the therapeutic agents entrapped in the polymer. The patent described methods for producing the precursor ketene acetals which are used in producing the bioerodible polymers. One of the methods for producing the ketene acetals which is described in the patent, involves the rearrangement of allyl acetals to produce the ketene acetals. The rearrangement methods proposed are characterized by low yields of the desired ketene acetal product and the ketene acetal product obtained in the rearrangement have a substantial content of impurities which are difficult to remove to a degree which produces a ketene acetal final product of sufficient purity to be useful in the production of the desired bioerodible polymers.
Pursuant to the method of the present invention, allyl acetals are rearranged to ketene acetals at high conversions and the ketene acetal product directly obtained by the method of the invention is readily purified to produce a polymer grade ketene acetal.